The present invention generally relates to programmable thermostats and, more particularly, to a temperature recovery system for an electronic programmable thermostat.
Attempts to develop improved heating and cooling systems generally focus on improved efficiency coupled with reduced costs. One technique which attempts to embody these concepts is temperature setback and recovery. Generally, setback refers to the concept of lowering the setpoint temperature of a thermostat during night-time periods or periods when the region or space controlled by the thermostat is unoccupied in order to reduce the energy required to heat the controlled region. A related concept called set-up refers to the raising of the setpoint temperature of a thermostat during periods of non-occupancy of the controlled region or space in order to reduce the energy required to cool the region. Finally, recovery refers to the concept of activating a heating or cooling system so as to raise (or lower) the ambient temperature of the controlled region or space by the end of the set-back (set-up) period to some predetermined temperature.
Studies conducted by the Department of Energy estimate that setting a thermostat back 10.degree. F. for two eight-hour periods during winter can reduce a user's energy costs by as much as 35%. Setting a thermostat up 5.degree. F. for two eight-hour periods during summer can reduce a user's energy costs up to 25%. However, an inefficient recovery system or the programming of too large a set-back or set-up temperature range can utilize as much or more energy than is saved by raising or lowering the temperature. This is especially true, for example, in multi-stage air conditioning systems which include heating systems employing both an energy efficient heating mechanism such as a heat pump and a less energy efficient auxiliary heating mechanism such as an electrical resistance-type heater. Excess use of the auxiliary heating mechanism can substanially increase energy costs. A similar situation also arises in muli-stage cooling systems.
As an example, a thermostat may be programmed to raise the ambient temperature of the controlled region from a set-back temperature of 60.degree. F. to a programmed temperature of 68.degree. F. by 6:00 A.M. In a thermostat having a built-in recovery system, the heating system will switch on at some time prior to 6:00 A.M. so that at 6:00 A.M., the ambient temperature will be 68.degree. F. In multi-stage heating systems, as noted above, this recovery time is very important. If the heating system is inefficiently operated during this period, excessive auxiliary heat may be utilized and no energy savings will result.